title: Intravenous contrast agent influence on thoracic computed tomography simulation investigated through a heterogeneous dose calculation method using 5-bulk densities.
abstract: OBJECTIVE
  Using 5-bulk-density heterogeneous dose calculation, we investigated whether contrast-enhanced (CE+) computed tomography (CT) will affect dose-calculation accuracy in the thoracic area.
  
  
  METHODS
  We analyzed 17 radiation-oncology patients who underwent thoracic CE+ CTs. Full-resolution CT and 5-bulk-density plans were generated using an adaptive convolution algorithm. Bulk densities for air, lung, fat, soft tissue, and bone were applied to regions identified by an isodensity segmentation tool. The population-averaged physical density of each region was calculated and compared with the reference value calculated from 66 noncontrast-enhanced (CE-) thoracic CT images. Using the 5-bulk densities, we created a new plan in which the physical densities of each area were forced to be the same as the CE- reference value, and we compared the dose-volume histograms (DVH).
  
  
  RESULTS
  Average physical density for the segmented air, lung, fat, soft tissue, and bone for CE+ were 0.14, 0.29, 0.90, 1.03, and 1.13 g/cm(3), and the reference values for CE- were 0.14, 0.26, 0.89, 1.02, and 1.12 g/cm(3), respectively. In all the cases, the normal-tissue DVH agreed to better than 1%. In 15 cases, DVH of the planning target volume (PTV) agreed to better than 3%. In 2 patients, >3% difference in the PTV dose was observed.
  
  
  CONCLUSIONS
  Only 2 patients with a strong injection artifact in the PTV or beam showed >3% discrepancy in the target dose. When using CE+ CT for treatment planning, strong injection artifacts must be excluded.
authors.affiliation: Department of Radiology, Juntendo University Urayasu Hospital, Japan. anyusaike@yahoo.co.jp
authors.forename: Anneyuko I
authors.initials: AI
authors.lastname: Saito
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Li
authors.forename: Chihray
authors.initials: C
authors.lastname: Liu
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Olivier
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Kyougoku
authors.forename: James F
authors.initials: JF
authors.lastname: Dempsey
mesh_terms: D000328:Adult; D000368:Aged; D016477:Artifacts; D003287:Contrast Media; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D008297:Male; D008875:Middle Aged; D013902:Radiography, Thoracic / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D003287:Contrast Media